The p53 tumor suppressor plays a central role in controlling cell cycle progression and apoptosis and is an attractive cancer therapeutic target because its tumor suppressor activity can be stimulated to eradicate tumor cells. Recent studies have suggested that stimulation of the p53 activity may be a powerful strategy for the treatment of the majority of hormone-refractory prostate cancer. In p53 wild-type cancer cells, the p53 activity is effectively inhibited by its endogenous inhibitor, the human murine double minute 2 (MDM2) oncoprotein by multiple mechanisms. A new therapeutic approach to stimulation of the activity of p53 is through nhjbition of its interaction with the MDM2 protein using non-peptide small-molecule MDM2 inhibitors. Design of non-peptide small-molecule inhibitors of the MDM2-p53 interaction is being intensely pursed as a new cancer therapeutic strategy. In the last two years, with the support of the University of Michigan SPORE grant, we have designed and developed a class of highly potent, non-peptide, orally available, smallmolecule inhibitors of MDM2. Based upon our promising in vitro and in vivo results, we are advancing our most promising lead compound into human clinical trials as a new therapy for the treatment of human cancer. Our long-term transitional goal in this SPORE renewal project is to develop a highly potent and promising small-molecule inhibitor of the MDM2-p53 interaction (hereafter called MDM2 inhibitor) as a new therapy for the treatment of advanced human prostate cancer. Toward this goal, we will carry out the following specific Aims: Aim 1: Determination of the in vitro activity, specificity and molecular mechanism of action of our potent MDM2 inhibitors in a panel of prostate cancer cell lines and normal cells. Aim 2: Determination of the in vivo antitumor activity and molecular mechanism of action of our potent MDM2 inhibitors in animal models of human prostate cancer and examination of any toxicity to animals. Aim 3: Performance of a Phase II clinical trial of our clinical lead compound in prostate cancer patients with androgen-independent disease. Successfully carried out, this SPORE project will pave the way for the development of an entirely new class of molecularly targeted anti-cancer therapy for the treatment of advanced prostate cancer.